Development of an electrothermal MEMS mirror based two-photon microscopy probe

Two-photon microscopy (TPM) has shown its great impact in studying neuronal activity of live animals. Commercial TPM systems require the animals under study to be restrained under the microscope and the 3D images are obtained typically by using bulky galvo scanning mirrors, which limits the flexibility of animal brain imaging to a large extent. To study freely moving animals, miniaturization of the optical scanning system is the key. In this work, a miniature TPM probe has been developed based on an electrothermal MEMS mirror that can be driven under low voltage. The MEMS mirror has an initial tilt angle after fabrication, and its footprint is 3 mm x 4 mm and reflective mirror plate is aluminumcoated with an equivalent diameter of 2.5 mm. This MEMS probe can be directly adapted to a commercial TPM system. In addition to the MEMS mirror for laser beam scanning, inside the MEMS probe head there are a fixed mirror to fold the laser beam and a high NA polymer lens for focusing. This miniature probe can realize an FOV of 3.5°, or a scanning range of 150 μm. This MEMS probe head is compact with a size of 8 mm x 16 mm, which can be further scaled down.